POWER CONVERSION APPARATUS

This invention relates generally to power conversion apparatus and more specifically, although not exclusively, to power conversion apparatus for powering a refrigeration unit such as those which are towed by vehicles, for example trucks or lorries.

Such refrigeration units require a reliable and/or consistent amount of power in order to ensure proper functionality. It is known to use a standalone diesel engine which drives a generator, which in turn powers the compressor of such a unit. The engine starts and stops based on the load requirements of the refrigeration unit. These refrigeration units also include a power cable for connection into a mains power supply of, say, 400V at 50Hz when the vehicle is parked.

Electrical generators known as alternators are generally coupled to and driven by an automobile engine by means of a flexible belt, whereby a portion of the mechanical power is converted into electrical power. This electrical power is then used to feed a battery. The battery powers ancillary equipment, for example electric windows and/or a fuel management system or the like, which require a direct current power supply.

The variable speed of the automobile engine causes variations in the power and/or frequency generated by the alternator. This issue is mitigated through the use of a battery, which regulates such fluctuations. However, standard alternators and batteries do not generate and/or store sufficient electrical power to drive a refrigeration unit, nor are they able to supply an alternating current to such a unit.

US6662586 discloses a vehicle with a refrigeration unit powered by the vehicle's own engine in place of a standalone system. The vehicle includes a pump, whose stroke volume can be regulated and which is mechanically connected to the vehicle engine, a motor to which fluid is supplied from the pump, a generator mechanically connected to the motor and a control device. The control device allegedly regulates the stroke volume of the hydraulic pump such that the magnitude of flow remains substantially constant.

However, the inventors have observed through detailed analysis that significant fluctuations of the pressure and flow rate supplied to the motor occur on occasion with this arrangement. Whilst the device appears to function properly, tests show that the pump and motor are often subjected to sharp variations in pressure and/or flow which can damage these devices over time.

It is therefore a general non-exclusive object of the present invention to provide an improved power conversion apparatus, particularly one which which at least mitigate the issues associated with the prior art. It is a further non-exclusive object of the invention to provide a power conversion apparatus which is able to draw power from a vehicle's engine more efficiently. It is a yet further non-exclusive object of the invention to supply this power to an existing refrigeration unit without the need to modify the unit or at least to minimise the extent of such a modification.

One aspect of the invention provides a power conversion apparatus comprising a variable displacement pump connectable to an automobile engine, a motor fluidly connected to the pump by a control valve, a generator operatively connected to the motor and a controller, wherein the pump induces a flow, in use, to drive the motor when the pump is driven by the engine thereby causing the motor to drive the generator, the controller being operable to control both the displacement of the pump and the position of the control valve for regulating the pressure and/or flow of fluid supplied to the motor from the pump to cause the generator to supply a predetermined alternating current frequency and voltage.

The provision of a control valve permits refined control of pressure and/or flow of fluid supplied to the motor from the pump, thereby reducing significantly the aforementioned fluctuations. This pressure and/or flow is preferably measureable, e.g. using one or more sensors.

For example, the controller may be configured or operable to vary the stroke volume of the pump, e.g. to provide a coarse control of the flow and/or pressure of fluid supplied to the motor, while the control valve may be configured to limit, e.g. using a limiting or protection or pressure relief valve, or adjustably vary or provide a fine control of, e.g. using a flow control valve such as a globe, ball, butterfly or servo valve, the flow and/or pressure of the fluid supplied to the motor. The valve may be coupled to an inlet and/or an outlet of the pump, for example to bypass, in use, all or a portion of the flow of fluid supplied from the pump to the motor and/or for controlling the load drawn by the pump from the engine.

A second aspect of the invention provides a kit, for example a retrofit kit, which kit may comprise one or more of the aforementioned elements and/or additional elements, e.g. for retrofitting the aforementioned apparatus onto an existing vehicle. Preferably, the

apparatus and/or retrofit kit comprises a housing within which may be located at least one of the motor, the control valve, the generator and/or the controller.

The controller is preferably arranged or operable to cause the generator to be driven, in use, at a predetermined speed, for example a substantially constant speed, for supplying the predetermined, for example a substantially constant, frequency. The controller may be operable to vary, for example adjustably vary, in use, the load drawn from the automobile engine based on a required load. Preferably, the controller is operable to supply a constant predetermined alternating current frequency and voltage, for example regardless of the load supplied by the generator.

The controller may further comprise a hydraulic or electrical or electronic circuit. The pump may comprise an axial piston pump, which pump may be operatively connected or connectable to the engine by a belt or a keyed or geared or splined drive means. Preferably, the pump is connected or connectable directly to the engine such as via a power take off of the engine, e.g. in order for the pump to be driven by the engine.

The pump preferably comprises a swash plate for regulating hydraulic fluid pressure and/or flow. The swash plate may be arranged or operable to cause the pump to supply a predetermined, for example a substantially constant, hydraulic pressure and/or flow. The apparatus or controller may comprise a pressure and/or flow sensor or sensors, for example hydraulic pressure and/or flow sensor or sensors, which may be arranged to measure the hydraulic pressure and/or flow supplied by the pump and/or supplied to the motor and/or through the hydraulic circuit. The pressure and/or flow sensor may be hydraulically or fluidly connected to or adjacent the inlet or outlet of the pump or the motor inlet or outlet and/or the hydraulic circuit.

The motor, e.g. hydraulic motor is preferably operatively coupled, e.g. close coupled, to the generator and/or may be arranged or operable to turn the generator at a predetermined, for example a substantially constant, rotational speed.

The controller preferably comprises a control unit, for example a hydraulic control unit or a microprocessor, microcomputer or programmable logic controller. The control unit is preferably arranged or programmed or programmable or operable to control the control valve, for example the position of the control valve, for regulating the fluid flow to supply, in use, a predetermined, e.g. a substantially constant or maximum, fluid flow rate to the

motor or output frequency of the generator. Thus, the stroke volume of the pump and/or the position of the control valve may be used to compensate for any variation in the rotational speed of the engine and/or in the flow rate supplied to the motor.

The pressure and/or flow sensor or sensors may be operatively connected to the controller. The apparatus or controller may also comprise a further sensor, for example a flow or speed sensor, for measuring a rotational speed of the motor and/or a drive shaft of the generator, which sensor may be operatively connected to the controller. Alternatively, the further sensor may comprise an electronic sensor arranged to measure the frequency of the electricity generated by the generator.

The apparatus may further comprise a load sensor which may be operatively connected to the controller. The load sensor may be arranged to detect a relay contact, for example which is representative of a demand from the refrigeration unit or ancillary equipment for power. The controller may be arranged or programmed or programmable or operable to receive a signal from the load sensor and to control the control valve in response to the signal.

Additionally or alternatively, the controller may be arranged or programmed or operable to adjustably vary, in use, the fluid pressure supplied by the pump, for example based on the measured and/or determined load, e.g. current, required or drawn by the refrigeration unit. The controller may be arranged or programmed or operable to calculate or determine the required stroke volume and/or valve position for the generator to generate the load required by the refrigeration unit and/or the load measured or determined, in use, by the load sensor and/or a predetermined load, for example substantially constant load.

A fourth aspect of the invention provides a controller for use in an apparatus as described above, the controller comprising an input means for receiving a feedback signal from a sensor indicative of the flow rate supplied by the pump or the speed of the motor or the output frequency of the generator and an output means for sending a command signal to the control valve or to the pump, wherein the controller is operable or specifically adapted to generate a command signal arranged to maintain a substantially constant flow rate or motor speed in response to a feedback signal received from the input means.

A further aspect of the invention provides an apparatus as described above with a refrigeration unit having a power cable electrically connected to the generator.

A yet further aspect of the invention provides an automobile comprising an apparatus as described above, wherein the pump is operatively connected or coupled to the engine of the automobile.

The automobile may be a truck or lorry. The refrigeration unit may be connected or secured to or mounted on the automobile or truck or lorry.

Another aspect of the invention provides a method of converting power, e.g. using a power conversion apparatus as described above, the method comprising converting mechanical power from an automobile engine into electrical power by controlling both the displacement of the pump and the position of the control valve to regulate the pressure and/or flow of fluid supplied to the motor from the pump to cause the generator to supply a predetermined alternating current frequency and voltage.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a partial perspective view of an apparatus according to the invention installed in a lorry; and

Figure 2 is a schematic view of the apparatus of Figure 1.

Referring to Figure 1 , there is shown an apparatus 1 according to the invention installed in a lorry 2 having an engine 3 to which the apparatus 1 is operatively connected and a refrigeration unit 4 electrically connected to the apparatus 1 by a power cable 40 (shown in Figure 2).

The apparatus 1 includes a pump 5, a controller 6, a motor 7 and a generator 8, which is an alternator in this embodiment. The pump 5 is of the variable displacement type with a swash plate (not shown) for varying the stroke volume according to load requirements and is coupled to the engine 3 by an endless drive belt 50 of the type known in the art. The pump 5 includes an inlet conduit 51 and an outlet conduit 52, both of which feed into the controller 6.

The motor 7 is coupled to the alternator 8 by an endless drive belt 70 of the type known in the art and includes an outlet conduit 71 and an inlet conduit 72, both of which feed into

the controller 6. The alternator 8 supplies power, in use, to the refrigeration unit 4 through the power cable 40. The alternator 8 is configured to provide a constant 400V supply.

Referring now to Figure 2, the controller 6 includes a control unit 60, a control valve 61 , a pressure sensor 62a, a flowmeter 62b and a fluid reservoir 65. The control unit 60 is electrically connected to the control valve 61 via a valve control cable 63 and to the pump 5 via a pump control cable 64 for sending control signals to adjustably control the position of the control valve 61 and the swash plate (not shown) respectively. The control unit 60 is also electrically connected to the pressure sensor 62a and to the flowmeter 62b by first and second feedback cables 66a, 66b respectively. The pressure sensor 62a is connected to an outlet of the control valve 61 and the flowmeter 62b is connected to an inlet of the fluid reservoir 65.

The outlet conduit 52 of the pump 5 is fluidly connected to the inlet of the control valve 61 and the inlet conduit 72 of the hydraulic motor 7 is fluidly connected to the outlet of the control valve 61. The outlet conduit 71 of the hydraulic motor 7 is fluidly connected to the inlet of the reservoir 65 and the inlet conduit 51 of the pump 5 is fluidly connected to an outlet of the reservoir 65..

The hydraulic pressure measured by the pressure sensor 62a functions as a load sensor by permitting the control unit 60 to detect an increase in demand from the generator 8 which causes an increase in resistance within the motor 7, thereby increasing the pressure measured by the pressure sensor 62a. The fluid flow measured by the flowmeter 62b is indicative of the speed of the motor 7 and, accordingly, the output frequency of the generator 8. Thus, the flow of hydraulic fluid supplied to the hydraulic motor 7, and hence the speed of rotation of the motor 7, may be controllably varied.

In this embodiment, the refrigeration unit 4 requires a constant voltage (400V) and frequency (50Hz). The control unit 60 is therefore arranged to regulate the frequency supplied by the alternator 8 by firstly varying the position of the swash plate (not shown) to vary the stroke volume of the pump 5 according to load requirements sensed by the pressure sensor 62a and secondly comparing the flow rate measured by the flowmeter 62b with a desired flow rate and varying the position of the control valve 61 to adjust the flow rate of fluid supplied to motor 7 as required to ensure a substantially constant rotational speed.

The controller 6 is programmed to ensure that a predetermined flow rate is supplied to the motor 7, thereby resulting in a predetermined rotational speed, in the case of this embodiment 1500rpm. This predetermined rotational speed results in the generator 8 supplying electrical power at the aforementioned 50Hz frequency.

It will be appreciated that an increase or decrease in the load drawn by the refrigeration unit 4, and therefore by the generator 8, will cause the position of the swash plate (not shown) and of the control valve 61 to change. Thus, the magnitude of the mechanical power transferred from the engine 3 by the apparatus is automatically regulated to match the load required by the refrigeration unit 4.

The apparatus is therefore able to supply a constant voltage and frequency at any engine speed, for example when the engine 3 is idling or running at full speed.

Tests have shown that this arrangement greatly reduces the overall fuel consumption and noise generation as compared to the aforementioned arrangement which utilises a standalone diesel engine. In addition, the reduction in moving parts results in the system being simpler and easier to maintain.

It will be appreciated by those skilled in the art that several variations to the specific embodiment disclosed herein are envisaged without departing from the scope of the invention. For example, the apparatus disclosed herein may be used for powering other ancillary equipment including, but not limited to, cranes, tanker heaters and/or automobile transportation equipment. Also, the pump 5 may advantageously be coupled to a power take off (not shown) of the engine, for example an engine dry power take off.

Moreover, the control valve 61 may be hydraulically or pneumatically controlled.

The alternator 8 or other type of generator 8 may be configured to provide a different voltage and/or frequency, for example a constant 480V and frequency of 60Hz. The controller 6, 106 may be replaced by any suitable means, for example a programmable logic controller.

Additionally or alternatively, the controller 6 may include a flow meter fluidly connected to the inlet conduit 72 of the hydraulic motor 7.

The refrigeration unit 4 may be replaced by any other device requiring a substantially constant voltage and frequency and/or may be used with any suitable automobile.

It will be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.